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Thread: Fork mount CPC 8" Edge vs. 8" Edge on AVX Mount

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    Default Fork mount CPC 8" Edge vs. 8" Edge on AVX Mount



    New to astronomy and have a few questions. I doing investigation for my next purchase and need opinions. How much difference in time is there to set up a fork mounted 8" Edge compared to an 8" Edge on the AVX mount? Can a fork mount be modified to receive other scopes. For instance, I have an Orion ED 80mm. I might get into AP in the future, just not sure at this point.

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    Default Re: Fork mount CPC 8" Edge vs. 8" Edge on AVX Mount

    The CPCs are a twin fork design, so not designed with the intention of taking the OTA off and mounting something else - unlike the single arm SE scopes that use a standard dovetail mount and would let you use other (short) OTAs.

    The usual method, with a twin fork scope, is to add a dovetail rail on each side of the SCT OTA, and piggyback a small OTA on top with counterweights underneath.

    For visual use, setup of an alt-az fork mount is a bit simpler - just put the mount + OTA on the tripod, and then do the alignment - point it at your alignment stars and off you go, no need to figure out where north is. and the alt-az mount keeps the eyepiece in a convenient position while observing.

    With an EQ mount (or a fork mount used on a wedge) it's a little more complicated - you need to get at least a reasonable polar alignment (pointing the axis at the celestial pole) to start off with - so you'll need to figure out where north is. With a manual - or driven - EQ mount, a rough polar alignment is all you need to track fairly well; not sure how accurate you need to be to get a goto EQ to do good gotos - and then run through a similar point at bright stars alignment for the goto setup. and the design of an EQ mount means the eyepiece moves around more than with an alt-az mount.

    For long exposure AP, you really need to use an EQ mount or add a wedge for a fork mounted scope (which tilts it so it works like an EQ mount) - running one in alt/az mode limits you to around 30s exposures due to field rotation - which can get you images, but it's a lot easier (and will go fainter) with a wedge that lets you expose much longer (and autoguide).

    Also for long exposure AP, you really need an accurate polar alignment - which may take a while to adjust, check, and readjust.

    Overall weight for an EQ mount is probably more, since you have counterweights for the scope, but breaks down into lighter pieces (since with the twin fork designs you have to move the OTA and mount together). This probably isn't a big issue with an 8", but can be significant with larger scopes - especially as you get older.

    For long exposure imaging, the general concensus seems to be that it's easier with an EQ mount than a fork mount - for one thing, you can swap between your ED80, which will be easier to start off with, and the SCT, for a bigger image scale when you've got the hang of things.

    So, if you think you may want to get into long exposure imaging, I'd go with the EQ mount - but for visual only (with maybe some lunar/planetary imaging) I think you'd find an alt-az fork mount more convenient.

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    Default Re: Fork mount CPC 8" Edge vs. 8" Edge on AVX Mount

    Time required to set up: For visual use the fork mount is a snap.. 2 parts..the tripod and the Mount/Ota combination...
    with the Gen you also needed the tripod BUT the mount itself is not connected to the OTA..so you have 3 parts involved PLUS the counterweights... more individual parts BUT nothing even remotely as heavy as the Fork Mounted mount/Ota combination

    It takes more time to set up the Gem but not very much more time..
    Align the scope : well you can align a fork mounted scope effortlessly even while seated or standing..with the Gem you "may" have to get down on your knees to polar align the mount..after you balance the darn thing.. (no big deal however)
    Using the scope...the eyepiece on a fork mounted scope will only move up and down along a maybe 6 inch path between the horizon and at Zenith... With a Gem the eyepiece can end up almost anywhere so you may have to do a little bending or stretching etc... Agan normally this is not a bid deal especially with a Sct or Refractor

    Your ED 80 will have to be piggybacked on top of the OTA if you use a fork mount...easy to do ...

    The fork mount is not going to accept any other OTA then the one it came with..(not easily or quickly anyway ) The Gem mount can hold either separate or both at the same time..again with the 80 piggybacked on top ..

    I will be 70 my next birthday and although I do own a couple Gem mounts both gather dust for the most part ...just way too "hard" on this old guys body top much kneeling bending and twisting just to get my eye in position to even look into the eyepiece.....So I use either of my 2 fork mounted scopes 20 times as much because when I relax under the stars I want to be comfortable (and avoid my Chiropractor the next day)

    I have absolutely no interest in AP although you sure can do short exposure work with the fork mount and long exposures are possible when you add a Wedge to the mount ...

    To be honest IF I were not sure I would NOT be buying with AP in mind ...NOT now and not before I experimented with what I have...(and I also would not spend the extra money for an edge scope either) ..

    Bob G
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    Default Re: Fork mount CPC 8" Edge vs. 8" Edge on AVX Mount

    Thank you Bob327: This is exactly wat I was looking for. My problem is trying to buy a scope that can do most of what I want to do with the easiest setup time. I also realize that I want to use the scope as much as possible and know I will hesitate to use it if the setup is too long and difficult.

 

 

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